In conventional machine tools requiring a high degree of precision, it is conventional to employ precision ground lead screw assemblies. Such a lead screw assembly typically includes a lead screw into which a recessed, spiral-shaped race has been ground, and a set of ball bearings positioned in the race. Using such an assembly, the machine tool operator may control the position of the lead screw to within less than 10.sup.-3 inch. However, conventional precision-ground lead screw assemblies are very expensive, and typically cost on the order of $1000 per assembly.
Less expensive lead screw assemblies (which typically cost less than one-tenth the price of a conventional precision-ground lead screw assembly) include machine-rolled lead screws. Because the pitch of the thread (or ball bearing race) of a machine-rolled screw is subject to relatively large manufacturing tolerances, it has not been possible for a machine tool operator to control the position of a machine-rolled lead screw sufficiently accurately for purposes of high-precision machining. Until the present invention, it had not been known how to position inexpensive screws (manufactured with a wide range of size and shape tolerances) with extreme precision.